active transport

• cells take up molecules and ions and keep them in high concentrations
• active transport: the net movement of molecules or ions out of the cell through the cell membrane against a concentration gradient, using energy from respiration
• the cell membrane contains carrier proteins
• carrier proteins span the cell membrane and provide means by which ions and molecules can enter or leave a cell by active transport
• first the molecule or ion combines with a carrier protein

  • energy from respiration enables the carrier protein to change its shape to carry the ion or molecule to the inside of the membrane
  • the molecule or ion is released to the inside of the membrane
  • the molecule or ion is released to the inside of the membrane and the carrier protein reverts to its original shape
• • epithelial cells lining the vili in the small intestine and the kidney tubules absorb glucose by active support
  • these cells have high rates of respiration to provide energy for this active transport
  • active transport relies upon respiration to take up ions or molecules against a concentration gradient